The Atom
Matter and Energy
The Atom
Part I: Modeling Atoms
Everything on Earth is made of matter. All of this matter is
made from tiny particles that we cannot see with the naked
eye – or even with the most powerful optical microscope.
These tiny particles are called atoms. Everything on this
planet – including you – is made from unique combinations
of atoms.
So, what exactly is an atom? What makes up an atom? How much mass does an individual atom
have? What makes one atom different from another atom? To answer these questions we will first
look at the overall structure of an atom and then build some model atoms to look for clues in the
patterns that appear.
Procedure:
1.  Cut out one (p+) circle from the strip given to you by your teacher. It represents a subatomic
particle called a proton. Color it yellow and glue it in the nucleus of the hydrogen atom found in
Part I of your Student Journal.
2.  Draw one VERY small, red dot between the nucleus and outer edge of the electron cloud in the
hydrogen atom. Just a dot will do. This dot represents a subatomic particle called an electron
(e-).
3.  Cut out two more (p+) circles from the strip given to you by your teacher. Color them yellow and
glue them in the nucleus of the helium atom found in Part I of your Student Journal.
4.  Cut out two (n0) circles from the strip given out by your teacher. They represent subatomic
particles called neutrons. Color them blue and glue them in the nucleus of the helium atom.
Overlapping is fine such that you still see parts of all four circles.
5.  Draw two VERY small, red dots (e-) between the nucleus and outer edge of the electron cloud
in the helium atom.
6.  Use your colors to make a color key for the protons, neutrons, and electrons.
As you built the models of a hydrogen and helium atom, you should have noticed some differences
between the protons, neutrons, and electrons, or subatomic particles. Subatomic particles are the
particles that are smaller than an atom. You should have noticed that there were two regions in the
atom, the nucleus and the electron cloud. The protons and neutrons are located in the nucleus
and the electrons are located in the electron cloud.
Please continue to the next page.
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The Atom
Matter and Energy
Part I: Modeling Atoms, continued
The mass of atoms and their subatomic particles is measured in Atomic Mass Units, or amu. A
proton and a neutron each have a mass of 1 amu. An electron is much smaller with a mass of
1/2000 amu. Because the mass of an electron is so small, their mass is not counted when
determining the total mass of an atom.
You probably noticed that you used different symbols to represent each of the subatomic particles.
The proton was represented by (p+). The + sign represent the positive electrical charge of a
proton. The electron was represented by (e-). The – sign represents the negative electrical charge
of an electron. The neutron was represented by (n0). The 0 sign represents the neutral electrical
charge of a neutron.
Complete the “Properties of Subatomic Particles” table in your Student Journal and then answer
the Part I questions.
Part II: Atom Patterns
We are well on our way to understanding atoms, the building blocks of our universe. We learned
the following:
•  Protons and neutrons make up the mass of an atom and are found in the nucleus.
•  Electrons do not contribute significant mass to an atom but do make up the volume of an atom
since they are found in the electron cloud.
•  The overall charge of the nucleus is positive because of the positive protons (p+) and neutral
neutrons (n0).
•  The charge of the electron cloud is negative because of the negative electrons (e-).
•  Protons, neutrons, and electrons are subatomic particles. Atoms are different from each other
because the numbers of their subatomic particles are different.
Let’s look closer at the mass and electrical charge of an atom.
Continue to the next page.
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The Atom
Matter and Energy
Part II: Atom Patterns, continued
Mass: Units for the mass of an atom are amu, Atomic Mass Units. We learned in Part I that each
proton contributes 1 amu, each neutron contributes 1 amu, and electrons are so small that they do
not contribute to the mass of an atom. One way to determine the mass of an atom is to simply
count the total number of protons and neutrons of the atom. The diagram of the hydrogen atom
that you built had one proton in the nucleus so the mass of this hydrogen atom is 1 amu. The
diagram of the helium atom that you built had two protons and two neutrons in the nucleus so the
mass of this helium atom is 4 amu.
Electrical charge of an atom: To determine the electrical charge of an atom simply count the
number of positive protons and the number of negative electrons, then add these two numbers
together. The hydrogen and helium atoms that you built in the diagrams did not have a charge. For
example: the hydrogen atom had one positive proton and one negative electron, resulting in (+1) +
(-1) = 0. The helium atom had two positive protons and two negative electrons, resulting in (+2) +
(-2) = 0. As long as the number of protons and electrons are equal, the atom is without charge or
neutral.
Use the information in the table below to make a model of a lithium atom and a model of a
beryllium atom in your Student Journal. Use the (p+) circles, colored yellow, to represent protons;
the (n0) circles, colored blue, to represent neutrons; and small red dots to represent electrons (e-)
for each model in your Student Journal.
Subatomic Par-cles Found in One Atom of the Elements Lithium and Beryllium Element Number of Protons Number of Neutrons Number of Electrons Lithium 3 4 3 Beryllium 4 5 4 After you build the models of a lithium and beryllium atom, complete the charts and questions in
Part II of your Student Journal to explore the properties of the subatomic particles.
Complete all questions in the Student Journal.
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